The present invention relates generally to cathodic protection, and more specifically to an impressed current cathodic protection system of the type employing a photovoltaic (PV) solar powered system to protect metallic structures, such as piers made of steel or other iron bearing material, installed in electrolytic media such as sea water or soil, from electrochemical corrosion and deterioration. This system uses an external dedicated direct current (DC) as the power source to develop and maintain a negative potential between one or more of a series of electrodes external to the structure be the protected, and the structure to be protected. The electrodes and the structure to be protected preferably should be within the same area of the galvanic series prior to the application of power because this facilitates polarization and minimizes anode corrosion. By applying the DC current to the electrodes, they become positive anodes from which the applied current flows. This impressed current flows out of the anodes, is conducted through the electrolytic medium, and is received by the surface of the structure to be protected, which structure becomes transformed into the negative electrode or cathode. Thus, polarization of the structure to be protected is considered to have occurred. Because it is well known in this technology that electrochemical corrosion occurs where the current leaves the anode metal surface to enter the ambient electrolyte, the anodes begin to corrode and those nearby surfaces that receive the current will not corrode, provided that a sufficient electrical potential is maintained between anode and cathode. Steel and cast iron structures are considered to become fully cathodically protected when the polarized potential of the structure is about -0.850 volt or more negative, with respect to a copper-copper sulfate reference electrode. Silver-silver chloride electrodes are more frequently used where they are required to be submerged in seawater because unlike the copper-copper sulfate electrode, they are not subject to contamination by seawater.
Anodes commonly used in impressed current systems are high-silicon cast iron with chromium added for improved resistance to the chloride attack of seawater.
In cathodic protection (CP) systems and technology, because it has been determined that by impressing a steel structure with the aforesaid -0.850 v negative potential or slightly more, the structure was considered to be cathodically well protected, then it became the logical and customary practice to maintain the potential at or about -0.850 v to -0.950 v to conserve energy, reduce energy costs and other operating costs such as minimizing the deterioration of the anodes. To obtain valid interpretation, the potential measurements must be corrected for IR drop through the electrolyte and metallic paths, by measuring the polarized potentials, usually -0.100 v to -0.300 v or more negative depending on the electrolyte, type and condition of the structure, temperature and other variables. Because of the usual use of readily available AC-DC rectifier systems to generate and maintain these adequate potentials on a continuous basis, and because of the reported potential for adverse effects, to be described, believed to be caused by the application of greater power to generate negative potentials above the approximate -0.950 v level, there was no impelling reason to explore or experiment with methods or apparatus to use higher negative potentials. This practice was further reinforced due to the possible disadvantages discovered by the limited trials of the higher negative potentials, particularly in laboratory tests, which were (1) causing of possible disbondment of various protective coatings preapplied to the structures and (2) the tendency due to absorption of atomic hydrogen to cause embrittlement, more particularly to high strength steel, or blistering and thereby prematurely weaken the structure's integrity. This phenomenon is seldom observed in the field because high strength steel is not generally used for steel structures in electrolytes such as sea water and pipe lines in soil. This prior art practice continued because it is considered axiomatic in CP systems that under the so-called instant-off conditions, the negative (cathodic) polarization potential will decay or drop within one second according to NACE, by about -0.100 v, to 0.300 v, or more, followed by further decay upon extending the off condition time, thus strengthening the belief that it was not possible to maintain the requisite beneficial negative potential and thus not possible to achieve adequate cathodic protection by any PV solar-powered CP system without an auxiliary backup power means (usually a battery).
While the prior art has many solar power applications, including cathodic protection, none of the systems or related methods are without battery backup systems that provide continuous DC power and have not suggested methods or ways of preconditioning or polarizing the structure or equipment to be protected by the temporary initial one time only use of a DC power generating source to impress the structure with significantly greater negative potentials over a selected extended time period. By my new procedure, the higher level negative polarized potentials developed are longer lived, or decay more slowly during periods of inclement weather and nighttime conditions, until their rebuilding upon receiving the benefit of the renewable solar panel generated DC current. This has been done successfully without any battery backup system for over two years.
As stated above, impressed current cathodic systems have required the use of rectifiers and other related complex circuitry and components to help assure a continuous DC power supply. Alternatively, electric motor or wind or any engine driven DC generator sets, DC welders, batteries, thermoelectric cells, and solar cells accompanied by backup battery systems, have been used to try to provide the requisite continuous DC current. These are not cost effective and many would adversely impact the environment, particularly when attempting such installations in remote areas or where continuous electrical power is not readily available.